an audio file creation technique that converts an analog signal into an 8-bit digital signal, similar to regular pulse code modulation (PCM), but it transmits voice communications at less than half or one fourth the speed of regular PCM communications.
Asymmetric Digital Subscriber Line (ADSL)
A high speed digital subscriber line technology that can use ordinary telephone lines for downstream data transmission of up to 6 Mbps and 576-640 Kbps for upstream transmissions.
Basic Rate Interference (BRI) ISDN
An ISDN interface that consists of three channels. Two are 64 Kbps channels for data, voice, and video transmissions. A third is a 16 Kbps channel used for communications signalling.
broadband ISDN (BISDN)
Currently under development and not widely implemented, this technology provides a data transfer rate of 155 Mbps and higher.
A protocol used to encrypt passwords, such as server account passwords that are transferred over a WAN.
On an ISDN Network that uses T-carrier communications, this means the communications circuit lasts for the duration of the communications session and is used exclusively by the two connected devices until it is terminated.
Compressed Serial Line Internet Protocol (CSLIP)
An extension of the SLIP remote communications protocol that provides faster throughput than SLIP.
data circuit equipment (DEC)
On an X.25 network, a packet switch or access device to a PDN.
An X. 25 transmission mode that does not use a particular communications channel, which often results in data arriving in a different order than it was sent, because each datagram may follow a different route to the destination.
data link connection identifier (DLCI)
Identifies an individual virtual connection on a frame relay network.
data terminal equipment (DTE)
On an X. 25 network, terminals, workstations, servers, and host computers that operate on a packet-switching network. DTE devices are sometimes called terminals, regardless of the actual device that is used.
digital subscriber line (DSL or xDSL)
A technology that uses advanced modulation technologies on existing telecommunications networks for high-speed networking between a subscriber and a telco, and that has communication speeds up to 55 Mbps.
Distributed Queue Dual Bus (DQDB)
An SMDS interface that consists of two shared fiber optic media. Both fiber optic cables are attached to the customer premises equipment at one end and to the vendor switch at the other.
Used in ISDN, this communications method transmits data on the line in two directions at the same time. The two way simultaneous transmissions often cause reflections (echos) of the transmitted signal. ISDN uses an echo canceler to overcome the reflected signals.
A communications protocol that relies on packet switching and virtual connection technology to transmit data packets, and that achieves higher transmission rates by leaving extensive error-checking functions to intermediate nodes.
frame relay assembler / disassembler (FRAD)
Also called a frame relay access device, specialized equipment often in the form of a module (card) in a switch or router that converts packets from the local network (LAN) into a format that can be transmitted over a frame relay network, and vice versa.
G.lite Asymmetric Digital Subscriber Line (G.lite ADSL)
A Plug and Play compatible version of ADSL that transmits at 500 Kbps upstream and 1.5 Mbps downstream.
High Bit-Rate Digital Subscriber Line (HDSL)
A form of high-speed digital subscriber line technology that has fixed upstream and downstream transmission rates of either 1.544 or 2.3 Mbps.
Integrated Services Digital Network (ISDN)
A standard for delivering data services over telephone lines, with a current practical limit of 1.536 Mbps and a theoretical limit of 622 Mbps.
Integrated Services Digital Network Digital Subscriber Line (IDSL)
A DSL version that is compatible with a Digital Loop Carrier device that may be used on some telephone networks. IDSL Provides upstream and downstream communications at 144 Kbps.
Link Access Procedure-Balanced (LAPB) protocol
Employed in X.25 communications, a protocol that is used to set up and discontinue virtual connections over the WAN.
Link Access Procedure D channel (LAPD)
Also referred to as the Q.921 protocol, specifies the frame format for ISDN Layer 2 communications.
Link Access Protocol for Frame Mode Bearer Services (LAPF)
The frame relay communications layer that corresponds to the OSI Data Link layer.
An extension that is added to the frame relay frame for additional functions, such as handling multicasting.
local management interface (LMI) protocol
Enables frame relay to determine when to create a new virtual circuit, when to delete a virtual circuit that is no longer in use, or identify a virtual circuit that has failed.
Network Termination Unit (NTU)
On an ISDN network this device provides a U interface for an incoming ISDN line and an S/T interface to connect to ISDN devices, such as computers, ISDN fax machines, and ISDN telephones.
High speed Ethernet, such as Gigabit or 10 Gigabit Ethernet, carried on fiber optic cable and used for MAN's.
packet assembler / disassembler (PAD)
A device that encapsulates a packet into X.25 format and adds X.25 address information. The PAD removes the X.25 format information when the packet reaches its destination LAN.
On an ISDN network that uses T-carrier communications, packet mode means that several circuits can be used during a communications session, and each connected device is assigned an address and sequence number at the start of the session to ensure that data arrives at the correct database.
Password Authentication Protocol (PAP)
A protocol that is used to authenticate an account password when accessing a server, host computer, or directory service over a WAN.
permanent virtual circuit (PVC)
Used in X.25, a communications channel that stays connected at all times, even when nodes are not communicating.
permanent virtual connection
Used in frame relay, a continuously available path between two points.
Plug and Play (PnP)
Ability of added computer hardware, such as an adapter or modem, to identify itself to the computer's operating system for installation and to enable automatic configuration.
Point-to-Point Protocol (PPP)
A widely used remote communications protocol that supports TCP/IP, NETBEUI, and IPX/SPX communications over WAN's.
Point-to-Point Tunneling Protocol (PPTP)
A remote communications protocol that enables connections to networks, intranets, extranets, and VPNs through the Internet.
Primary Rate Interface (PRI) ISDN
An ISDN interface that consists of switched communications in multiples of 1.536 Mbps.
public data network (PDN)
A network that is typically privately owned and operated and that provides data communications services to members of the public.
pulse code modulation (PCM)
An audio file creation technique that converts an analog audio signal into an 8bit digital signal. PCM is used in frame relay audio communications and on the Internet.
Rate Adaptive Asymmetric Digital Subscriber Line (RADSL)
A high peed data transmission technology that offers upstream speeds of up to 1 Mbps and downstream speeds of up to 7 Mbps. RADSL uses ADSL technology, but enables the transmission rate to vary for different types of communications, such as data, multimedia, and voice.
Serial Line Internet Protocol (SLIP)
Designed for UNIX environments for point to point communications between computers, servers, and hosts using TCP/IP.
Signaling System 7 (SS7)
A WAN protocol for telecommunications networks that used to set up the fastest route between two telecommunications carriers.
A voice communications method over data communications lines, such as over frame relay, in which voice transmissions are sent during moments of inactivity (silence) on the lines.
A device that is about the size of a credit card and can be plugged into a computer. The advantage of a smart card is that it can be equipped with a digital signature, access keys, password access, and personal identification number (PIN) to control login access and access to files and data.In addition, it provides extra security when used for remote access over a public or private telecommunications line.
A variety of ADPCM that is tailored to work over ISDN and frame relay.
Switched Multimegabit Data Services (SMDS)
Also called Switched Megabit Data Services, this is a transport method developed by regional telephone companies to provide cell-based, high-speed communications over MANs and WANs.
switched virtual circuit (SVC)
Used in X.25, a communications channel that is created for the duration of a communications session and that normally exists on a medium that can handle multiple channels.
switched virtual connection
Used in frame relay, a means of connecting for a transmission session by sending a special control signal between two nodes to establish communication. Once the communication is finished, the call control signal issues a command for each node to disconnect. This type of connection enables the network or T-carrier provider to determine the data throughput rate.
Symmetric Digital Subscriber Line (SDSL)
A form of digital subscriber line technology that is often used for video conferencing or online learning. It offers a transmission speed of 384 Kbps for upstream and downstream communications.
Symmetric High Bit-Rate Digital Subscriber Line (SHDSL)
Also called G.shdsl, a DSL technology that can be transmitted over one or two wires and that can reach up to about 4 miles (over two wires). The upstream and downstream rates can vary in the range of about 192 Kbps to 2.3 Mbps.
synchronous optical network (SONET)
A fiber optic communications technology that is capable of high speed (over one gigabit per second) data transmission. Networks based on SONET can deliver voice, data and video.
time compression multiplexing
Used in ISDN, a communications method that sends 16 to 24 bit blocks of data in alternating digital bursts. There is a quiet period between bursts to allow the line to settle before the next burst. The first burst goes in one direction, followed by a pause. The pause is followed by a burst in the opposite direction.
Very High Bit-Rate Digital Subscriber Line (VDSL)
A digital subscriber line technology that works over coaxial and fiber optic cables yielding 51-55 Mbps downstream and 1.6-2.3 Mbps upstream communications.
virtual tributary (VT)
In SONET communications, a separate envelope of data. the VT determines how a carrier signal is mapped into the SONET frame.
A method for transmitting voice communications by converting them from an analog format into a digital format, thus creating digital audio files that are played back to the listener.
voice over frame relay
Using frame relay to transmit voice signals as a way to replace the need for regular telephone communications.
An older, very reliable packet switching protocol for connecting remote networks at speeds up to 2.048 Mbps. The X.25 protocol defines communications between DTEs and DECs.
XON/XOFF flow control
An older flow control technique that uses a Ctrl+S to pause transmission and a Ctrl+Q to restart transmission.